Electrophotographic laser printing employs a toner containing pigment components and thermoplastic components for transferring a latent image formed on selected areas of the surface of an insulating, photoconducting material to an image receiver, such as plain paper, coated paper, transparent substrate (conducting or insulative), or an intermediate transfer medium.
There is a demand in the laser printer industry for multi-colored images. Responding to this demand, designers have turned to liquid toners, with pigment components and thermoplastic components dispersed in a liquid carrier medium, usually special hydrocarbon liquids. With liquid toners, it has been discovered that the basic printing color (yellow, magenta, cyan, and black) may be applied sequentially to a photoconductor surface, and from there to a sheet of paper or intermediate medium to produce a multi-colored image.
The liquid toner must be dispersed uniformly in the liquid hydrocarbon carrier medium, since the toner tends to settle out. Such uniform dispersion requires some sort of agitation, which must be provided without permitting leakage of the liquid. Thus, leakage must be minimized to the extent possible, in order to prevent loss of liquid and all the attendant problems associated with spillage of liquid inside an electrographic printer.
Use of a mechanically-coupled external pump to internal rotary agitation requires running seals, which can, over time, degrade and hence become prone to cracks and wear, which enable leakage of the liquid to occur. Conventional gear-coupled drive shafts also have the problem of lining up orthogonal to the pump and agitation device, due to space limitations in the printer.
While it is desired to use vent holes to equalize the pressure inside the cartridge as the toner is used up, such vent holes, of course, also provide an opportunity for leakage of the liquid toner. To circumvent the problem of employing vent holes, collapsible poly-bags have been employed, which collapse as liquid toner is consumed. The collapse of the poly-bag, however, leaves no room for a rotary agitation device inside the cartridge after the bag has partially collapsed.
Thus, there remains a need for a liquid toner cartridge which permits rotary agitation while eliminating most if not all of the foregoing problems.